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A user on an AR waits for a long time to obtain an IP address through DHCP

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When the AR is used as the user access device (the WAN uplink interface connects to the Internet and the LAN downlink interface connects to the intranet), STP is enabled by default. After a user connects to an AR, the interface is in Discarding state in the first 30s. DHCP Request messages are discarded. After 30s, DHCP messages can be exchanged.
You are advised to enable STP to prevent network flapping caused by STP convergence.

Other related questions:

By default, STP is enabled on the device used as the user access device (WAN-side interface connects to the Internet and LAN-side interface connects to the internal network). The device interface is in Discard state 30s after users connect to the device. DHCP Request packets are discarded. DHCP packets are processed after 30s.
It is recommended that STP be disabled to prevent network flapping caused by slow STP convergence.

Users on S series switches except S1700 switches obtain IP addresses slowly because the STP function is enabled on interfaces of the switches. (By default, STP is enabled on all interfaces of a switch.)
When an interface of a switch goes Up, STP convergence is performed for about 30 seconds. During STP convergence, the switch discards all received packets including DHCP request packets sent from users. As a result, the users obtain IP addresses slowly.
You can resolve the problem using either of the following methods:
- Run the stp edged-port enable command to configure the switch interface connected to users as an edge interface.
If the stp bpdu-protection command has been configured on the switch, the edge interface of the switch goes Down when the switch receives attack BPDUs. To enable the edge interface to automatically go Up, run the error-down auto-recovery cause bpdu-protection interval interval-value command.
- If no physical ring topology exists on the network, you can run the stp disable command on the switch globally or on the switch interface connected to users.
Additionally, when the switch functions as a DHCP server and after you remove and reinstall the network cable, the PC obtains an IP address after 1 minute. The problem may be caused by a software bug. When you remove and reinstall the network cable, the PC sends DHCP Request messages to the DHCP server. In earlier versions of a switch, software cannot properly process this event.

Perform the following steps to locate the fault:
1. Check whether the AP is configured to obtain an IP address through DHCP.
2. Check whether the Layer 2 link between the AP and DHCP server is working properly.
3. Run the display ip pool name ip-pool-name used command on the DHCP server to check whether the AP has obtained an IP address.

Perform the following steps to solve the problem:
Connect the Internet.
If the Internet is not connected, install the SSL certificate. The procedure is as follows:
In the Internet Explorer address bar, click Certificate Error:
Click View certificates.
In the Certificate dialog box that is displayed, click the General tab and Install Certificate.
Click Next.
In the Certificate Store area, select Place all certificates in the following store:
Click Browse, select Trusted Root Certification Authorities in the Select Certificate Store dialog box, and click OK.
Click Next.
Click Finish.
If the Internet is not connected and you do not want to install the SSL certificate, disable the Update Root Certificates component.
The procedure on the Windows XP operating system is as follows:
Open Control Panel and choose Add or Remove Programs > Add/Remove Windows Components. The Windows Components Wizard dialog box is displayed.
Clear Update Root Certificates.
Click Next.
Click OK.
The procedure on the Windows 7 operating system is as follows:
Choose Start.
Click Run and enter gpedit.msc.
Click OK or press Enter.
Choose Computer Configuration > Administrative Templates > System > Internet Communication Management > Internet Communication settings.
Double-click Turn off Automatic Root Certificates Update and click Enabled.
Click OK.